Persons wear respiratory masks (also referred to as "face masks" and "filtering face masks") for two common purposes: (1) to prevent contaminants from entering the wearer's respiratory system; and (2) to protect others from being exposed to pathogens and other contaminants exhaled by the wearer. In the first situation, the respirator is worn in an environment where the air contains substances harmful to the wearer--for example, in an auto body shop. In the second situation, the respirator is worn in an environment where there is a high risk of infection--for example, in an operating room.
Investigators believe that comfortable masks are much more likely to be worn and therefore are more beneficial from a safety standpoint. Because safety of the wearer and others is a primary concern in respirator development, investigators in the respirator art have directed efforts towards producing masks that are comfortable to wear (see e.g., U.S. Pat. No. 5,307,796).
Some respiratory masks are categorized as "disposable" because they are intended to be used for relatively short time periods. These masks are typically made from nonwoven fibrous webs. Fibers that protrude from the web have caused wearer discomfort by creating a tickling sensation that makes wearers want to scratch that area of their face. When a mask is worn to protect the wearer from breathing impurities in the air or to protect others from infection, the wearer becomes confronted with the choice of tolerating the itching sensation or risking exposure of themselves or others to potentially dangerous contaminants.
Disposable respiratory masks generally fall into two different categories, namely, fold-flat masks and molded masks. Fold-flat masks are packed flat but are formed with seams, pleats and/or folds that enable them to be opened into a cup-shaped configuration. Molded masks, however, are preformed into a desired face-fitting configuration and generally retain that configuration during use.
Molded respiratory masks are commonly made from thermally bonding fibers. Thermally bonding fibers bond to adjacent fibers after being heated and cooled. Examples of face masks formed from such fibers are shown in U.S. Pat. Nos. 4,807,619 and 4,536,440. The face masks disclosed in these patents are cup-shaped masks that have at least one layer of thermally bonding fibers. The layer of thermally bonding fibers is termed a "shaping layer", "shape retaining layer" or "shell" and is used to provide shape to the mask and support for a filtration layer. Relative to the filtration layer, the shaping layer may reside on an inner portion of the mask (adjacent to the face of the wearer), or it may reside on an outer portion or on both inner and outer portions of the mask. Typically, the filtration layer resides outside the inner shaping layer.
In some cases, all of the layers of material are assembled together before the shaping layer is molded so that all of the layers are subjected to the molding procedure. In other cases, only the material for the shaping layer is molded and the other layers are applied afterwards. In those cases, to assist in applying the other layers to the pre-molded shaping layer and to reduce creasing, the other layers may first be preformed into a cup-shape, for example by cutting and seaming.
A molded respiratory mask that is formed by applying one or more layers of material to a pre-molded shaping layer is described in, for example U.S. Pat. No. 4,807,619. Masks that are formed by assembling all the layers of the mask together before the molding procedure are described in, for example U.S. Pat. Nos. 4,536,440; 4,807,619; 4,850,347; 5,307,796 and 5,374,458. Masks of this type offer the advantage of generally being simpler and less costly to produce especially when manufactured by a continuous process.
The present invention is concerned with providing a direct-molded respiratory mask that enables effective respiratory protection to be achieved while offering a good degree of comfort and that can be manufactured in a comparatively simple and cost-effective manner.